1. Field of the Invention
This invention relates to a method for producing an image forming member having sensitivity to electromagnetic waves such as light (herein used in a broad sense, including untraviolet rays, visible light, infrared rays, X-rays and gamma-rays).
2. Description of the Prior Art
Photoconductive materials, which constitute image forming members for electrophotography in solid state image pick-up devices or in the field of image formation, or photoconductive layers in manuscript reading devices, are required to have a high sensitivity, a high SN ratio (Photocurrent (I.sub.p)/(I.sub.d)), spectral characteristics matching to those of electromagnetic waves to be irradiated, a rapid response to light, a desired dark resistance value as well as no harm to human bodies during usage. Further, in a solid state image pick-up device, it is also required that the residual image should easily be treated within a predetermined time. Particularly, in case of an image forming member for electrophotography to be assembled in an electrophotographic device to be used in an office as office apparatus, the aforesaid harmless characteristic is very important.
From the standpoint as mentioned above, amorphous silicon (hereinafter referred to as a-Si) has recently attracted attention as a photoconductive material. For example, German OLS Nos. 2,746,967 and 2,855,718 disclose applications of a-Si for use in image forming members for electrophotography, and German OLS No. 2,933,411 discloses an application of a-Si for use in a photoelectric converting reading device.
However, under the present situation, the photoconductive members of the prior art having light-receiving layers constituted of a-Si are further required to be improved in a balance of overall characteristics including electrical, optical and photoconductive characteristics such as dark resistance value, photosensitivity and response to light, etc., and environmental characteristics during use such as humidity resistance, and further stability with lapse of time.
For instance, when the above photoconductive member is applied in an image forming member for electrophotography, residual potential is frequently observed to remain during use thereof if improvements to higher photosensitivity and higher dark resistance are scheduled to be effected at the same time. When such a photoconductive member is repeatedly used for a long time, there will be caused various inconveniences such as accumulation of fatigues by repeated uses or so called ghost phenomenon wherein residual images are formed.
Further, according to a large number of experiments by the present inventors, a-Si as the material constituting the photoconductive layer of an image forming member for electrophotography, while it has a number of advantages, as compared with inorganic photoconductive materials such as Se, CdS, ZnO and the like or organic photoconductive materials such as PVCz, TNF and the like of prior art, is also found to have problems to be solved. Namely, when charging treatment is applied for formation of electrostatic images on the light-receiving layer of an image forming member for electrophotography having a light-receiving member constituted of a mono-layer of a-Si which has been endowed with characteristics for use in a solar battery of prior art, dark decay is markedly rapid, whereby it is difficult to apply a conventional electrophotographic process. Moreover, this tendency is further pronounced under a humid atmosphere to such an extent in some cases that no charge is retained at all before development time.
Further, a-Si materials may contain as constituent atoms hydrogen atoms or halogen atoms such as fluorine atoms, chlorine atoms, etc. for improving their electrical, photoconductive characteristics, boron atoms, phosphorus atoms, etc. for controlling the electroconduction type, or carbon atoms, nitrogen atoms, oxygen atoms and others for improvement of other characteristics or for the purpose of lamination of another layer for separate function. Depending on the manner in which these constituent atoms are contained, there may sometimes be caused various problems in the image forming member formed.
Especially, the layer containing carbon atoms is very important, since it can be utilized for a wide scope of purposes in addition to making higher dark resistances, such as improvement of adhesion, controlling of the optical forbidden band gap, imparting of layer hardness, formation of insulating layer, etc. Accordingly, depending on these purposes, it is frequently required to change the content of carbon atoms to a great extent. For this reason, according to the prior method, in which the source for supplying silicon atoms and the source for supplying carbon atoms have been found in separate starting materials, a large number of parameters must be operated and optimization of such parameters was encountered by an extreme difficulty.
Also, during formation of a deposited film by discharging decomposition such as by glow discharging, etc., when the deposited film is constituted of a plurality of constituent atoms and the sources for supplying respective constituent atoms are different molecules, it is preferred for obtaining a deposited film having good characteristics that the decomposition energies of the respective starting molecules by discharging should be substantially the same. However, hydrocarbon gases such as CH.sub.4 or C.sub.2 H.sub.4 conventionally used for formation of a film of carbon containing hydrogenated silicon (hereinafter written as Si.sub.x C.sub.1-x (H)) are higher in decomposition energy under discharging of molecules for supplying carbon atoms into the deposited film than the decomposition energy of a silane type gas which is the supplying source of silicon atoms, whereby it is difficult to obtain a good deposited film. Even if a good film may be obtained, inconveniences were frequently caused such that the preferably preparation conditions were restricted extremely.
For avoiding such a problem, it is also known to use a gas containing silicon atoms and carbon atoms in one molecule, for example, a gas of Si(CH.sub.3).sub.4 and the like. In this case, the content ratio of silicon atoms to carbon atoms in the deposited film is restricted by the constituent atomic content ratio in the molecule, and the hydrogen atoms appear to be supplied into the deposited film in the form previously added to carbon atom as --CH.sub.3, whereby there is the fear of disadvantageous excessive introduction of hydrogen atoms. Thus, this method was also inconvenient for obtaining desired characteristics of the deposited film for a wide scope of purposes.
In view of the above points, the present invention contemplates the achievement obtained as a result of extensive studies made comprehensively from the standpoints that selection of the starting material suitable for formation of Si.sub.x C.sub.1-x (H) film, which plays an important role in constitution of the a-Si type image forming member, is important and it is based on discovery of a starting material for supplying silicon atoms, carbon atoms and hydrogen atoms suited for this purpose.